The subject matter disclosed herein generally relates to Holographic Data Storage (HDS) media. More specifically, the embodiments of the present invention relate to techniques associated with preformatting and recording data in micro-holographic data storage media.
Conventional data storage technology employs magnetic and optical data storage devices. Conventional methods involve storing individual bits of data using distinct magnetic or optical changes on a surface of the storage medium.
In a holographic data storage medium, data is stored in volume holograms resulting from the interference of a signal beam and a reference beam. Such a recording technique requires the use of specialized components, such as spatial light modulators and charge coupled detectors with very stringent mechanical tolerances to ensure satisfactory operation. Secondly, the optical drive system required for recording data in volume holographic data storage medium is not backward compatible with conventional DB/DVD/CD optical drive systems.
Another type of holographic data storage medium, known as a micro-holographic data storage medium obviates the above mentioned drawbacks. Such a medium has relaxed tolerances and therefore is easier to manufacture and handle. Also, the micro-holographic storage medium is compatible with conventional BD/DVD/CD optical drive systems. The micro-holographic data storage medium does not require the use of a completely different optical drive system for use, unlike the volume holographic type data storage medium. Typically, the data density on the micro-holographic data storage medium can be increased by the use of an objective lens with higher numerical aperture (NA). However, diffraction efficiency (DE) from a micro hologram (bit) for a beam directed through an objective lens of higher NA, is low. As a consequence, the S/N ratio of the read signal obtained from an objective lens with higher numerical aperture will be low. A beam directed through an objective lens of lower NA increases DE from a micro-hologram, thereby reducing the data density in the storage medium.